JPH10331792A - Structure of intake part of centrifugal compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce vane passing frequency (BPF) noise by providing a guide vane having a low height at the inner surface of shroud just before an impeller leading edge of a centrifugal compressor, and thereby giving an auxiliary turning movement whose turning direction is reverse to the rotating direction of impeller to air flow flowing along the outer periphery of an intake part. SOLUTION: Guide vanes 4 having a low height are provided on the inner surface of shroud 2 just before an impeller leading edge 1a. The vane 4 is straight and inclined at the angle of θ to a straight line parallel to an impeller axis 11 so that it gives auxiliary turning movement whose turning direction is reverse to the rotational direction of impeller to air flow flowing on the outer peripheral side of an intake part 10. Accordingly, when the quantity of flow changes from a large level to a small level, change in a flow-in angle at the vicinity To outer peripheral end of the edge 1a is made smaller than the case where such auxiliary turning is not given thereto. Consequently, the maximum value of difference between the flow-in angle and inlet vane angle can be restrained small, resulting in restraining of BPF noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a suction part of a centrifugal compressor, and more particularly, to a blade passing frequency noise of a suction part in a centrifugal compressor of a vehicle supercharger.
ncy (hereinafter referred to as “BPF”).

[0002]

2. Description of the Related Art A supercharger (turbocharger) for a vehicle guides high-temperature and high-pressure exhaust gas from an engine to rotate a turbine, and drives a centrifugal compressor by the turbine to boost the intake air of the engine. This is to improve the output. FIG. 3 is a partially cutaway perspective view of such a supercharger for a vehicle. In the figure, 1 is an impeller, 2 is a shroud,
3 is a centrifugal compressor and 10 is a suction unit.

The impeller 1 is an open type as shown in FIG. In this figure, the impellers with long and short blades are shown, but some blades have long blades. In FIG. 4, 1a is the impeller leading edge of the long blade, 1b
Is an impeller leading edge of the short blade, and 1c is a hub.

[0004]

Such a turbocharger has a problem of noise. Among the noises is the BP of the centrifugal compressor
There is F noise. BPF noise means that when the flow rate flowing through the centrifugal compressor changes and the air inflow angle deviates from the inlet blade angle, the separation of the flow causes a frequency near the impeller leading edge to be twice the number of blades of the rotation speed. This is noise caused by pressure fluctuations.

[0005] The inventors of the present application have actually measured such BPF noise, and the results will be described. FIG. 5A shows a measurement position, and FIG. 5B shows a measurement result. FIG. 5B shows the measurement points on the horizontal axis and the level of the pressure fluctuation on the vertical axis, and the number of rotations is 80,000 rpm.
For m, 90,000 rpm and 100,000 rpm, the level of pressure fluctuation at each measurement point is shown. As shown in the figure, it can be seen that the level of the pressure fluctuation is highest at the measurement point I, that is, at the position of the leading edge 1a of the long blade.

The present invention has been devised in view of the above-described problems of the prior art, and has been devised to reduce the BPF noise that increases when the operating flow rate deviates from the design flow rate over the entire range of the operating flow rate. And by reducing the deviation of the inlet blade angle with the inlet blade.

[0007] An inlet guide vane is conventionally known for changing the inflow angle of the impeller inlet.
The inlet guide vanes are provided radially throughout the suction section for the purpose of adjusting the flow rate, and the angle can be adjusted, making it difficult to apply to small centrifugal compressors such as superchargers for vehicles. That, if the angle is fixed, the characteristics of the centrifugal compressor will change, the purpose of the present invention,
The configuration and effects are different.

[0008]

To achieve the above object, the structure of the suction part of the centrifugal compressor of the present invention is such that a short guide vane is provided on the inner surface of the shroud immediately before the impeller leading edge of the centrifugal compressor, and the outer periphery of the suction part is provided. A pre-swirl in the direction of rotation of the impeller is given to the flowing air flow.

The height of the guide vane is preferably less than half the radial height of the impeller leading edge, and higher than the gap between the impeller leading edge and the inner surface of the shroud.

Next, the operation of the present invention will be described. A short guide vane provided on the inner surface of the shroud immediately before the impeller leading edge imparts pre-swirl in the direction opposite to the rotation of the impeller to the airflow flowing on the outer peripheral side of the suction portion. Then, when the inflow rate changes from the large flow rate to the small flow rate, the change in the inflow angle near the outer peripheral end of the impeller leading edge is
It is smaller than when no pre-turn is given. Therefore,
The maximum value of the difference between the inflow angle and the inlet blade angle can also be suppressed small, and the BPF noise can be suppressed low.
Since the pre-turn is limited to the flow near the outer circumference of the suction part,
The provision of the guide vanes hardly affects the characteristics of the centrifugal compressor. By providing the guide vanes, the inflow angle can be kept within ± 3 ° of the inlet blade angle.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1A is a partial cross-sectional view of the structure of the centrifugal compressor suction section of the present invention, and FIG. 1B is a development view taken along the line BB of FIG. 1A. Note that, in these figures, the same parts as those described in FIGS. 3 and 4 are denoted by the same reference numerals, and redundant description will be omitted. In FIG. 1, reference numeral 4 denotes a guide vane which is provided on the inner surface of the shroud 2 immediately before the impeller leading edge 1a and is short. 5 is a vector of the peripheral speed of the impeller leading edge. The guide vane is a straight line inclined by θ ン with respect to a straight line 11a parallel to the impeller axis 11, as shown in FIG. Preliminary turn is given.

Next, the operation of the present embodiment will be described. FIGS. 2A and 2B are diagrams showing velocity vectors of the airflow flowing into the impeller leading edge 1a, wherein FIG. 2A shows a case without guide vanes, and FIG. 2B shows a case with guide vanes. In FIG. 2, reference numeral 5 denotes a vector of the peripheral velocity at the outer edge of the leading edge. In FIG. 2A, 6 and 7 are vectors of the absolute inflow velocity and the relative inflow velocity when the flow rate is large, and 8 and 9 are the vectors of the absolute inflow velocity and the relative inflow velocity when the flow rate is small. α is the inflow angle when the flow rate is large, and β is the inflow angle when the flow rate is small. FIG. 2B shows each vector when a pre-turn of an angle θ is given to the absolute inflow velocity in a direction opposite to the impeller rotation direction, and each vector is displayed with a subscript a.

As apparent from these figures, the difference (αa−βa) between the inflow angle at the time of the large flow rate and the small flow rate when the pre-swirl is given is the inflow angle when the pre-swirl is not given. (Α−β). Therefore, the difference between the inflow angle and the blade entrance angle can be reduced with respect to the change in the flow rate, and the separation area in the vicinity of the impeller leading edge 1a can be reduced. Accordingly, the pressure fluctuation level in the shroud 2 near the impeller leading edge 1a can be kept low. Since the BPF noise is caused by this pressure fluctuation level, low noise can be achieved.

Further, unlike the conventional inlet guide vane, the height of the guide vane is short, so that the air flow only in the vicinity of the shroud 2 on the outer periphery of the suction part 10 is merely pre-rotated, and the fluid performance of the centrifugal compressor is reduced. Has little effect.

The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the gist of the invention. For example, although the guide vane has been described as a straight blade, the guide vane may be a curved blade as long as the angle on the outlet side is the same.

[0016]

As described above, the structure of the suction portion of the centrifugal compressor according to the present invention is such that a short guide vane is provided on the inner surface of the shroud immediately before the impeller leading edge, and the air flow near the outer edge of the leading edge is pre-rotated. (1) BPF noise can be reduced. (2) Unlike the conventional inlet guide vanes, the guide vanes hardly affect the fluid performance of the centrifugal compressor. It has excellent effects.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a drawing of the structure of a centrifugal compressor suction part of the present invention, (A) is a partial cross-sectional view, and (B) is a BB view of (A).

FIG. 2 is a drawing of a velocity vector of an air flow flowing into an impeller leading edge, (A) without a guide vane, (B) with a guide vane.

FIG. 3 is a partially cutaway perspective view of a turbocharger.

FIG. 4 is a perspective view of an impeller.

5A and 5B are explanatory diagrams of a BPF noise measurement test, in which FIG. 5A is a diagram showing a measurement location, and FIG. 5B is a graph showing a measurement result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Impeller 1a Impeller leading edge 2 Shroud 3 Centrifugal compressor 4 Guide vane

Claims (2)

[Claims] The present invention is characterized in that a short guide vane is provided on the inner surface of a shroud immediately before an impeller leading edge of a centrifugal compressor, and a pre-swirl in a direction opposite to a rotation direction of the impeller is given to an air flow flowing around the suction portion. Centrifugal compressor suction section structure. 2. The height of the guide vane is less than half the radial height of the impeller leading edge,
2. The structure of the centrifugal compressor suction part according to claim 1, wherein the clearance is higher than a gap between the impeller leading edge and the inner surface of the shroud.